Role control is no longer actively maintained. Please see Auto Assign Role as a replacement.
Role Control, allows administrators to grant users the ability to add themselves to a specific role. When used in conjunction with Taxonomy Access Control this provides an easy way for users to give themselves a simplified view of your Drupal installation.
This is very useful if your site serves a population who might be overwhelmed by the mass of content on the site if they are dropped into everything at once. It lets them explore a sanitized site until they are comfortable, at which point they can check a box on their user edit page and gain access to the remainder of the site.
The administration section is setup so the administrator can specify all text associated with the checkbox on the user edit page so the user doesn't know they've been added to a
specific role, but might see something like "Enable premium content", or "Show me the videos."